Boron industrial synthesis

Variations in the conditions used for the nitrolysis of hexamine have a profound effect on the nature and distribution of isolated products, including the ratio of RDX to HMX. It has been shown that lower reaction acidity and a reduction in the amount of ammonium nitrate used in the Bachmann process increases the amount of HMX formed at the expense of Bachmann and co-workers ° were able to tailor the conditions of hexamine nitrolysis to obtain an 82 % yield of a mixture containing 73 % HMX and 23 % RDX. Continued efforts to provide a method for the industrial synthesis of HMX led Castorina and co-workers to describe a procedure which produces a 90 % yield of a product containing 85 % HMX and 15 % RDX. This procedure conducts nitrolysis at a constant reaction temperature of 44 °C and treats hexamine, in the presence of a trace amount of paraformaldehyde, with a mixture of acetic acid, acetic anhydride, ammonium nitrate and nitric acid. Bratia and co-workers ° used a three stage aging process and a boron trifluoride catalyst to obtain a similar result. A procedure reported by Picard " uses formaldehyde as a catalyst and produces a 95 % yield of a product containing 90 % HMX and 10 % RDX. 

The industrial synthesis of BN is based on a two-stage process. In the first stage, conducted at approximately 900 °C, a boron source such as B2O3 (boron oxide) or H3BO3 (boric acid) is converted in a reaction with a nitrogen source (mostly melamine or urea, sometimes even ammonia [NH3]) to form amorphous BN ... 

The discovery route varied little from the industrial synthesis. From bromopyridine 24, the boronic acid 30 was prepared in 88% yield via metal-halogen exchange and quenching the corresponding anion with BfOCHsls. Suzuki coupling with 2-bromopyridine 31 afforded the common intermediate 25. 

Continuous-Flow Stirred-Tank Reactors. The synthesis of j )-tolualdehyde from toluene and carbon monoxide has been carried out using CSTR equipment (81). -Tolualdehyde (PTAL) is an intermediate in the manufacture of terephthabc acid. Hydrogen fluoride—boron trifluoride catalyzes the carbonylation of toluene to PTAL. In the industrial process, separate stirred tanks are used for each process step. Toluene and recycle HF and BF ... 

The c-BN phase was first obtained in 1957 [525] by exposing hexagonal boron nitride phase (h-BN) to high pressures and low temperatures. A pressure of more than 11 GPa is necessary to induce the hexagonal to cubic transformation, and these experimental conditions prevent any practical application for industrial purposes. Subsequently, it has been found that the transition pressure can be reduced to approximately 5 GPa at very high temperature (1300-1800°C) by using catalysts such as alkali metals, alkali metal nitrides, and Fe-Al or Ag-Cd alloys [526-528]. In addition, water, urea, and boric acid have been successfully used for synthesis of cubic boron nitride from hexagonal phase at 5-6 GPa and temperature above 800-1000°C [529]. It has been... 

For the last four decades, there has been an exponential increase in the synthesis and usage of a number of organic and inorganic boron compounds in industry and academia. Due to the explosive growth of heterocyclic boron-containing compounds, this topic is covered as a separate chapter here. Previously, the subject of this chapter was covered in a subsection of Chapter 4.24 in CHEC-II(1996) (Sections 4.24.1.3.6 and 4.24.1.3.7). This chapter covers as much literature as possible, but the space restraints did not permit a comprehensive coverage of all literature. 

The synthesis of the angiotensin II inhibitor Losartan [38] (69, Scheme 16) fittingly illustrates the impact of DoM on current large-scale industrial practice. The powerful tetrazolyl DMG (67) is used in a 4-step sequence without isolation of intermediates to afford boronic acid 68 which, via a key Suzuki-Miyaura cross coupling, leads the commercial medicinal agent in multi-ton quantities. 

Typical industrial process for the synthesis of phenyl boronic acid from phenylmag-nesium bromide and boronic acid trimethoxy ester requires strict temperature control (—25 to —55 °C) to minimize the formation of side products. Recently, Hessel and coworkers reported that a micromixer (width 40 pm and depth 300 pm)/ tubular reactor system gave the phenyl boronic acid at high yield (>80%) even at higher temperatures (22 or 50 °C) with minimum amounts of the side products (Scheme 4.48) [66]. They also achieved a pilot-scale production by employing a caterpillar minimixer (width range 600-1700 pm and depth range 1200-2400 pm). 

The heteroboranes are derived ultimately from boranes, which, in turn, can be built up from lower molecular weight boron hydrides, the simplest of which is diborane, B2H6. There are a number of industrial processes described for the synthesis of diborane, most involving the reduction of boron trihalides with metal hydrides, as shown in equation (1). Other methods involve the reduction of trihaloboranes with group 1... 

In suitable cases the application of stoichiometric chiral auxiliaries may be advantageous even on the industrial kilogram-scale. Scheme 49 provides as an example the synthesis of a thromboxane antagonist (ICI D1542) via the Evans aldol strategy [114]. Thus, the chiral auxiliary 49-1 is converted into the amide 49-3 and then submitted to a boron mediated aldol addition leading to 49-4 in dias-tereomerically pure crystalline form. The auxiliary is removed by reduction and... 

This experimental protocol is also valid for most syntheses under high pressure, for example, the synthesis of diamond or cubic boron nitride in the laboratory or in industry. In the latter case, the high-pressure cell must be much larger (50 mm inner diameter) and it requires large belt-type equipment and a more powerful hydraulic press. 

Carbon in the structural form of diamond is the only element used industrially as a hard material. Each year about ten tons of natural diamond and about twenty tons of synthetic diamond (produced via high temperature high pressure synthesis) are marketed as hard materials. While pure diamond is transparent, a yellow tint results from the replacement of some carbon atoms by nitrogen, and a blue, yellow, or even green tint through substitution of carbon by boron atoms. Polycrystalline diamond with impurities, used as an abrasive, is often black. 

Silicon alloyed with a copper catalyst and promoter substances reacts with methyl chloride (at temperatures around 300 °C) to give a mixture of methylchlorosilanes in the industrial direct synthesis. Dimethyldichlorosilane represents the most important target in this process. Since Rochow [1] and Mtiller [2] discovered this direct synthesis route for the silicon-promoter-catalyst system, many investigations were done to increase the activity as well as the selectivity and to clarify the mechanism. Zinc, tin, and phosphorus, beside other substances, were found to give effects [3-6]. The goal of this research work is to find out whether there are relationships between the electronic effect of phosphorus, tin, boron, or indium doping of silicon and its reactivity as well as selectivity in direct synthesis. Characterization of the electronic state of the variously doped silicon relies on photo-EMF measurements. 

One distinguishes palladium(0)- and palladium(ll)-catalysed reactions. The most common palladium(O) transformations are the Mizoroki-Heck and the cross-coupling transformations such as the Suzuki-Miyaura, the Stille and the Sonogashira reactions, which allow the arylation or alkenylation of C=C double bonds, boronic acid derivates, stan-nanes and alkynes respectively [2]. Another important palladium(O) transformation is the nucleophilic substitution of usually allylic acetates or carbonates known as the Tsuji-Trost reaction [3]. The most versatile palladium(ll)-catalysed transformation is the Wacker oxidation, which is industrially used for the synthesis of acetaldehyde from ethylene [4]. It should be noted that many of these palladium-catalysed transformations can also be performed in an enantioselective way [5]. 

---